Project Summary Toxicological and epidemiologic studies have shown developmental neurotoxicity of polybrominated diphenyl ethers (PBDEs), a group of flame retardants (FRs) widely used in the U.S. and elsewhere. With the phase-out of PBDEs from the market since 2004, replacement FRs, including organophosphate flame retardants (OPFRs) and novel brominated flame retardants (NBFRs), are increasingly added to consumer products to meet flammability requirement. Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and Firemaster 550 (FM 550) are the most commonly used replacement FRs. TDCPP, also referred to as ?chlorinated tris?, is an OPFR once added to children?s sleepwear in the 1970s but later removed because of toxicity concerns. Triphenylphosphate (TPP) and various TPP analogs are OPFR components in FM 550, while 2-ethylhexyl- 2,3,4,5-tetrabromobenzoate (TBB) and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) are NBFR components in FM 550. TDCPP, TPP and FM 550 have been reported to alter thyroid hormone levels, reduce neuronal viability and replication, alter neuronal differentiation, cause abnormal embryogenesis and development, affect neurobehavior, and change gene expression levels and DNA methylation in experimental studies. Compared with experimental study evidence of OPFRs and NBFRs, there are significant gaps in our understanding of their developmental neurotoxicity in humans. We propose to examine developmental neurotoxicity of OPFRs and NBFRs using the Cincinnati-based Health Outcomes and Measures of the Environment (HOME) Study, an existing birth cohort of 410 children from prenatal to 12 years of age, with prenatal and postnatal exposure assessment, thyroid hormones, cognitive and behavioral tests, and neuroimaging data. We hypothesize that prenatal and postnatal exposures to OPFRs and NBFRs are associated with: 1) altered thyroid hormone levels in maternal, cord, and childhood serum samples; 2) decreased child cognitive function; 3) poorer child neurobehavioral functioning; and 4) adverse impact on brain structure, organization, and function identified by neuroimaging at age 12 years. The proposed research will be the first to comprehensively study developmental neurotoxicity of both OPFRs and NBFRs in children. Addressing neuroendocrinological, neurobehavioral, and neuroimaging aspects of brain development is highly innovative for this investigation. The findings will be of critical value to scientific community and policy makers evaluating potential impact of current-use replacement FRs on developing brain. The research is highly relevant to the National Institutes of Health mission to identify potential chemical exposures that disrupt brain development and provide critical data to inform prevention strategies.